WestJet has started contacting guests on those flights to let them know of the possible exposure, said airline spokeswoman Lauren Stewart in an email to The Huffington Post Canada.

"Health and safety is our top priority and we are working very closely with the Toronto Public Health and following its recommended protocol for managing this situation," she added.

Highly contagious

Measles is a highly contagious disease that spreads easily to those who are not immune or are vulnerable, such as infants, pregnant women and people with weakened immune systems, said the city news release.

Anyone who has not had two doses of a measles vaccine or who has not had measles in the past is at risk of infection.

Symptoms of measles include high fever, cold-like symptoms such as cough or runny nose, sore eyes or sensitivity to light, and a red rash lasting four to seven days.

Anyone experiencing those symptoms should contact their doctor as soon as possible, and not go to work or school, said Toronto Public Health.